1. Field of the Invention
The present invention relates to an ultrawideband antenna device of small dimensions to be used in the communications equipment.
2. Related Art to the Invention
With the success of second generation and third generation wireless communication the fourth generation (4G) or long term evolution (LTE) is now being developed. 4G/LTE mobile communications provide wideband multimedia services at high data rates.
The LTE specification provides downlink peak rates of at least 100 Mbps and an uplink of at least 50 Mbps and RAN round-trip times of less than 10 ms. LTE supports scalable carrier bandwidths from 1.4 MHz to 20 MHz and supports both frequency division duplexing (FDD) and time division duplexing (TDD). The next step for LTE evolution is LTE advanced and is currently being standardized in 3GPP release 10. The standard includes that five different terminal classes have been defined from a voice centric class up to a high end terminal that supports the peak data rates. All terminals will be able to process 20 MHz bandwidths. There is also increased spectrum flexibility with supported spectrum slices as small as 1.4 MHz and as large as 20 MHz. All frequency plans currently used by IMT systems will be used.
One of the research challenges in LTE is the broad frequency range i.e. 698 MHz to 2690 MHz, of the interface between the user equipment (UE) and the eNODE B. If standard half-dipoles or quarter wavelength monopole antennas were to be used, the size of the antenna would be about 21 cm or 10.5 cm for the low frequency range. This would appear too large for the application in the user equipment, mobile phones for example. Moreover, the bandwidths of standard dipole and monopole antennas are too narrow to cover the operating bands of 4G communications.
Different antenna designs have been suggested and used in the past, none of which have an ultrawideband characteristic covering the whole frequency range of 698 MHz to 2690 MHz.
For example, an antenna device in which an antenna element is formed of a linear conductor having two bent portions can be used in which a feeding terminal is disposed at a predetermined position of the antenna element and one end portion of the antenna element is grounded. An antenna device can also have an antenna element that is formed of a linear conductor having four bent portions. In this way, the antenna device can reduce an equipment area since the antenna element of the monopole antenna is bent.
Hence, these are bent monopoles which therefore need less length than straight monopoles. Branch antennas that operate within multiple frequency bands are also being utilized in the hand held radio telephones.
Branch antennas typically include a pair of conductive traces disposed on a substrate that serve as radiating elements and that diverge from a single feed point. The antenna generally includes a flat substrate having a pair of meandering radiating elements disposed thereon. The meandering radiating elements diverge from the feed point that electrically connects the antenna to RF circuitry within a user's equipment. Each of the meandering radiating elements is configured to resonate within a respective frequency band.
Branch antennas may transmit and receive electrical signals within in a band of frequencies that are too narrow for 4G operation. Furthermore, in order to decrease the size of a branch antenna, it is typically necessary to compress the meandering pattern of each radiating element, which typically narrows the frequency band within which the radiating element can operate. To solve this, an antenna including a flat dielectric substrate having a pair of radiating elements, e.g. conductive copper traces disposed in a surface thereof can be used.
The radiating elements branch from an electrical connector to a feed point that electrically connects the antenna to RF circuitry within a user's equipment (UE). Each radiating element has a respective meandering pattern with the respective electrical length that is configured to resonate within a respective frequency band, preferably one high and one low. A preferable material for use of the dielectric substrate is FR4 or polyimide. The dielectric substrate should have a dielectric constant between about 2 and about 4. The size and shape of the dielectric substrate is a tuning parameter. Dimensions of the high and low frequency band radiating elements may vary depending on the space limitations of the substrate surface. The bandwidth of the antenna may be adjusted by changing the shape and configuration of the meandering patterns of the high and low frequency band radiating elements.
In another example of an antenna it is a central principle that different branches of the multiple band antenna are resonant at different frequencies. The antenna branches are connected to a common port for exchanging signals between the antenna branches and the transceiver circuitry of a user's equipment (UE). The first branch is of a length and construction so as to have resonant frequencies in a first band, and the second branch is of a length and construction so as to have resonant frequencies in a second band. The antenna is tuned, for example at the time of manufacture, to an impedance of approximately 50Ω for both bands. Each antenna branch is comprised of a relatively thin flexible dielectric film and a strip antenna formed by a meandering metal line. The metal line can be formed by printing, etching, or other suitable methods. Because the film is a flexible material the printed film can be rolled into a generally cylindrical shape for use as an antenna branch. The cylinder could be partially open or completely closed, depending upon antenna design considerations. For example, the bandwidth of the antenna can be varied by varying the diameter of the cylinder. The meandering metal line is varied between the antenna branches such that the different antenna branches are resonant at different frequencies. Thus multiple resonances and multiple branches can be achieved by selecting appropriate strip dimensions and patterns for each branch. The antenna branches are similar to monopole antennas.
Unfortunately, branch antennas may transmit and receive electrical signals within a band of frequencies that is too narrow to satisfy the needs of LTE and 4G or that hardly has the margin to take into account the surrounds of a UE. Furthermore, in order to decrease the size of hand antenna, it is typically necessary to compress the meandering pattern of a radiating element.
Unfortunately, as the meandering pattern of a radiating element becomes more compressed, the frequency band within which the radiating element can operate typically becomes narrower.
Thus, in light of the demand for ultra wideband UEs and the problem with conventional antennas for such mobile communications equipment, a need exists for smaller UWB antennas that are capable of operating in the LTE/4G frequency range.
Furthermore, in recent years the usage of antennas in other fields than mobile communications has also increased. For example, there is an increasing need for antennas in the industrial field for, among others, machine to machine communication or in the medical device field for, among others, patient monitoring. Demand has also increased for antennas in the field of home appliances in the pursuit of home automation.
It follows that an antenna with improved wideband frequency characteristics and compact size is not only desired for mobile communication equipment, but also for non-mobile equipment.